1. Field of the Invention
The present invention relates to a distance-measuring equipment for measuring distance from a moving target such as a running automobile, with use of which the time required for calculation of the distance can be greatly reduced.
2. Description of the Prior Art
Conventionally, various distance-measuring equipments using image sensors have been widely known so far, a case in point being the one disclosed in Japanese Patent Publication No. 63-46363, and one embodiment thereof is described in a block diagram shown in FIG. 6. Referring to FIG. 6, the distance-measuring equipment has a left optical system and a right optical system respectively comprising lenses 1 and 2 disposed with a distance L corresponding to the length of a base line between the respective optical axes thereof, and image sensors 3 and 4 which are disposed at a distance f corresponding to the focal lengths of the lenses 1 and 2 on the optical axes respectively. The image of a target 5 at a distance R from the respective lenses 1 and 2 is focused on the image sensors 3 and 4 respectively by the lenses 1 and 2. Then, the respective image sensors generate image signals. AD converters (analog-to-digital converters) 6 and 7 convert the analog image signals into proportional digital image signals, and memories 8 and 9 store the digital image signals respectively. A microprocessor 10 processes the digital image signals stored in the memories 8 and 9 to determine the distance from the target 5.
In operation, the microprocessor 10 reads a picture element signal a1 representing a picture element at the upper left-hand corner of the image sensor 3 from the memory 8, reads a picture element signal b1 representing a picture element signal at the upper left-hand corner of the image sensor 4 from the memory 9, and then calculates the absolute value C11 of the difference between these two picture element signals a1 and b1 as shown in a formula; C11=.vertline.a1-b1.vertline.. Then the microprocessor 10 reads picture element signals a2 and b2 respectively representing picture elements next to the picture elements a1 and b1 at the respective upper left-hand corners of the image sensors 3 and 4, calculates the absolute value C12 of the difference between the picture element signals a2 and b2 as shown in a formula C12=.vertline.a2-b2.vertline., and then adds the thus calculated absolute value C12 to the absolute value C11 obtained in the preceding cycle of calculation. This procedure is repeated sequentially for all the picture elements of the image sensors 3 and 4 to obtain an accumulated value S1 as shown by a formula; S1=.SIGMA.C1i. Subsequently, the microprocessor 10 reads the picture element signal a1 representing the picture element at the upper left-hand corner of the image sensor 3 from the memory 8, reads a picture element signal b2 representing a picture element next to the picture element b1 at the upper left-hand corner of the image sensor 4, and then calculates the absolute value C21 of the difference between these picture element signals a1 and b2 as shown by a formula; C21=.vertline.a1-b2.vertline.. Then microprocessor 10 reads picture element signals a2 and b3 respectively representing picture elements next to the picture elements a1 and b2 of the respective image sensors 3 and 4, and then calculates the absolute value C22 of the difference between these picture element signals a2 and b3 as shown by a formula; C22=.vertline.a2-b3.vertline.. This procedure is also repeated sequentially for all the picture elements of the image sensors 3 and 4 to obtain the value S2, which is the accumulated total of the absolute values of the differences, by a formula; S2=.SIGMA.C2i.
Accordingly, the total sum Si of the absolute value of the differences between the picture element signals of the respective image sensors 3 and 4 can be obtained by repeating the same kind of procedure as above in which the picture element signals of the image sensor 4 to be compared with those of the image sensor 3 are shifted to the right for one picture element at each cycle of comparison procedure. By the way, since the relative dislocation of the right and left images is represented by the minimum value Sj of the above accumulated total value Si, if the minimum value Sj corresponds to the number of picture elements n, then the distance from the target 5 is determined by a formula: EQU R=f.multidot.L/n.multidot.p (1)
where R is the distance from the target 5, p is the pitch of the picture elements, f is the focal length of the lenses 1 and 2, and L is the distance between the optical axes of the lenses 1 and 2 corresponding to the length of the base line.
Since the conventional distance-measuring equipment is constructed as above, it is able to measure only the distance from a target on its optical axis, and accordingly in measuring the distance from a moving object, the distance-measuring equipment must be turned according to the movement of the moving target so that its optical axis coincides with the target. And further, since the calculation time necessary for comparison of the picture elements obtained from the respective image sensors 3 and 4 throughout the whole picture elements is substantially long, the equipment cannot be adopted for such systems as distance alarm device, an automatic tracking device and so forth, and therefore it is not either practical for a distance-measuring equipment for vehicles.